The cosmetic market has begun to include many active ingredients in formulations to help curb the effect of aging and skin damage. Unfortunately, the efficacy of some of these molecules is reduced due to the natural barrier properties of the skin membrane. In particular the outer most stratum corneum layer shows poor skin permeability of compounds that are hydrophilic, very lipophilic, of high molecular weight or charged.
For example, transdermal penetration of active molecules is especially relevant to products designed to protect skin from photoaging. In this case long UVA rays penetrate deep into the epidermis and produce free radicals which can cause long term health effects. Antioxidants are able protect the cells from this damage by scavenging free radicals and inhibiting oxidation reactions. However, research has shown that in order for many of active molecules, such as antioxidants to be effective they must also reside in the epidermis.
The most common technique to increase transdermal delivery is to use penetration enhancers. While many chemical penetration enhancers such as solvents work well to disrupt the lamellar lipid structure of the skin many of them are toxic, irritating, allergenic, or not suited to cosmetic formulations which cover large areas (unlike typical pharmaceutical transdermal patches).
Other techniques to increase transdermal delivery of active compounds rely on delivery systems such as liposomes in combination with solvents. U.S. 2006/0110439 discloses a delivery system containing liposomes and solvents to increase penetration of an active compound. U.S. Pat. No. 6,355,657 discloses a system for percutaneous delivery of the opioid loperamide that combines an organic solvent and fatty acid/fatty alcohol penetration enhancers, such as oleic acid, olleyl alcohol, ethoxydiglycol, laurocapram, alkanecarboxylic acid, dimethyl sulfoxide, polar lipids or n-methyl-2pyrrolidone.
While many cosmetic applications require the addition of penetration enhancers for efficacious actives, the enhancers must overcome the added challenges and needs of being safe, reversible and able to work in a cosmetic form or dose. In addition these enhancers must not interfere with the active molecule in such a way that compromises the molecule's activity. Thus, there is a need for compositions that increase the transdermal bioavailability of active compounds.